Conventionally, there is provided a spectroscopic device for measuring a characteristic of a substance by using an electromagnetic wave such as ultraviolet light, infrared light, a microwave, a terahertz wave or the like. Spectroscopy is classified into some methods depending on a physical amount to be measured by an electromagnetic wave. The methods include absorption spectroscopy and reflection spectroscopy. The absorption spectroscopy serves to transmit an electromagnetic wave through a sample to be a spectroscopic measurement target and to measure a physical property or a chemical property of the sample depending on a change in the electromagnetic wave which is caused by an intersection of the electromagnetic wave and the sample during passage through the sample. Moreover, the reflection spectroscopy is utilized for spectroscopic measurement of a material which does not transmit light therethrough, a material which scatters light or the like, and measures the property of the sample by analyzing light reflected from a sample surface.
Light is absorbed by a substance when energy of photon and an energy structure of a substance coincide with each other. For this reason, it is necessary to select a different light source or measurement technique in accordance with a phenomenon or structure to be observed in a sample serving as a measurement target. In general, an electromagnetic wave having a short wavelength (for example, ultraviolet light, infrared light, visible light or the like) is suitable for capturing a small structure or a strong interaction and an electromagnetic wave having a long wavelength (a terahertz wave or the like) is suitable for capturing a large structure or a weak interaction. Terahertz time domain spectroscopy (THz-TDS) serves to perform Fourier transformation over a time waveform of an electromagnetic wave obtained by directly measuring a waveform of a terahertz wave, thereby acquiring information about an amplitude and a phase of the terahertz wave.
A substance to be measured which is used as a spectroscopic measurement sample has gaseous, solid-like and liquid-like configurations and the like. Depending on the respective configurations, there is devised a method of arranging a substance to be measured in such a manner that an electromagnetic wave is transmitted properly. In order to perform measurement with high precision over a liquid-like sample, for example, a sample to be arranged in the spectroscopic apparatus is required to be formed so thinly that an electromagnetic wave is transmitted. In the case in which a liquid sample is subjected to spectroscopic measurement with a terahertz wave, particularly, it is necessary to perform the measurement by making a liquid into a plate-shaped uniform thin film and transmitting a terahertz wave through the plate-shaped part in order to prevent a reduction in an SN ratio of a measurement signal because of a great absorption effect of the terahertz wave through a water molecule.
In the measurement for a liquid sample, generally, the sample is inserted into a vessel (generally referred to as a solution cell) formed by a material for transmitting an electromagnetic wave, for example, glass and the electromagnetic wave is incident from an outside of the solution cell to measure the electromagnetic wave transmitted through the solution cell. When the liquid sample is inserted into the solution cell and is thus measured, however, spectroscopic information of a cell material is superposed as a noise on spectroscopic information of the liquid sample so that measurement of true spectroscopic information is disturbed.
In consideration of such a problem, conventionally, there is proposed an apparatus which is intended for enabling measurement of spectroscopic information with small noises without using a solution cell (for example, see Patent Documents 1 and 2). The apparatuses described in the Patent Documents 1 and 2 serve to use of a nozzle for directly causing the liquid sample to be thin-film shaped, and serve to jet a liquid sample from the nozzle by pressure of a pump, thereby generating a thin and flat plate-shaped liquid film.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2011-127950
Patent Document 2: Japanese Laid-Open Patent Publication No. 2015-219088